The present invention relates to an improvement of a cam bracket for supporting a camshaft on the cylinder head of an internal combustion engine.
In a comparable case of the art, as shown in the exploded perspective view of FIG. 7, a camshaft 1 is provided with cams 2, 2 to open and close the intake and exhaust valves of an engine. Also, the camshaft 1 is provided with two pieces of thrust plates 3, 3 at an interval in order to prevent the camshaft 1 from moving in its axial direction. On the front end of the camshaft 1 there is provided a cam sprocket 4, to which is transferred the rotating force from the crank shaft of the engine by a chain, belt or the like so as to rotate the camshaft 1.
On the journal surface 6 hollowed in the cylinder head 5 to fit the camshaft 1 there is formed an oil hole 7 to supply oil.
A cam bracket 8 is attached with bolts to the journal surface 6 so as to support the camshaft 1 for rotation. On both ends of the journal surface 6 on the front periphery of the cylinder head 5 there are formed sliding surfaces 51, 51 slidably to contact with the thrust plates 3, 3. Also, on the front and back sides of the front side cam bracket 8 there are formed sliding surfaces 52, 52 slidably to contact with the thrust plates 3, 3.
In this type of the structure there is a problem that the machining of the sliding surfaces 51 and 52 are difficult because of the requirement respectively to machine the sliding surfaces 51 and 52 in the condition that the cam bracket 8 is attached to the cylinder head 5 so that the sliding surface 51 and sliding surface 52 may be matched and formed as the same surface.
Further, because of the structure where the oil from the oil hole 7 is supplied through the journal surface 6 into the space between the thrust plates 3, 3 and the sliding surfaces 51, 52, the lubrication for the sliding surfaces 51, 52 has come late at the starting of the engine. Accordingly, there is a problem that it is necessary to determine the higher level of the supplying capacity at low rotation of the oil pump.
In another comparable case of the art, as shown in the exploded perspective view of FIG. 8, a camshaft 1 is provided with one piece of a thrust plate 3 and a thrust plate slot 53 to insert this thrust plate 3 for rotation is formed in hollow inside the journal surface 6 of the cylinder head 5. Also, a thrust plate slot 54 to insert this thrust plate 3 for rotation is formed in a cam bracket 8. Oil from an oil hole 7 is supplied through an oil groove 6a formed in hollow on the journal surface 6 to the thrust plate slot 53. In this type of the structure there is no need to increase the supply capacity at low rotation of the oil pump because of satisfactory lubrication for the circumference of the thrust plate 3 with the oil stored inside the thrust plate slot 53.
However, in this type of the structure, there is a problem that the machining involves difficulties because of the requirement precisely to machine the thrust plate slots 53 and 54.
Further, there is a problem that the structure increases in weight because of the requirement to use material for the structure that the thrust plate slots 53 and 54 cover the whole thrust plate 3.
In further comparable case of the art, as shown in the exploded perspective view of FIG. 9, a camshaft 1 is provided with one piece of a thrust plate 3 and a thrust plate slot 54 to insert this thrust plate 3 for rotation is formed in a cam bracket 8 only. The thrust plate slot 54, in particular, is formed in an apron 56 integrally formed on the back side surface of the cam bracket 8 and a cutaway surface 56a is formed on the upper side of the apron 56 so that the top end of the thrust plate 3 may project from the thrust plate slot 54.
In this type of the structure, the scattering oil in the vicinity of the camshaft 1 and thrust plate 3 can be stuck to the thrust plate 3, the machining of the thrust plate slot 54 is easy and the structure becomes light in weight. However, right after starting of the engine, in the situation that the oil may not scatter sufficiently in the vicinity of the thrust plate 3, the lubrication becomes short and any trouble such as seizure may occur. In order to prevent such trouble, it is necessary to provide an oil jet 55 or the like on the cylinder head 5 so as to spout out oil from this oil jet 55 toward the thrust plate 3. There is a problem that the pressure in the oil supply passage drops down because of this oil jet 55 so that it is necessary to increase the supply capacity of the oil pump.
The present invention is worked out in view of the above-described problems in the comparable cases of the art. It is an object of the present invention to provide a cam bracket that can be comparatively easily machined without much increasing in weight. It is another object of the present invention to provide a cam bracket that can sufficiently lubricate the vicinity of the thrust plate without increasing of the supply capacity of the oil pump. The subject matter of the present invention is a cam bracket adapted to support a camshaft for rotation in cooperation with a cylinder head and provided with a support portion having a slot for supporting a thrust plate of the camshaft for rotation, wherein an oil sump is formed in a hollow fashion on the upper surface of the support portion around the edge of the slot at least on one side in a rotation direction of the thrust plate.
Hence, during operation of the engine, it is possible that the scattering oil is stuck to the thrust plate to lubricate it and, also, the scattered oil is well gathered in the oil sump. Further, during starting of the engine, it is possible that the gathered oil is stuck to the thrust plate, so that the vicinity of the thrust plate is lubricated sufficiently and any seizure is satisfactorily prevented from occurring.
Further, in case that an oil sump is formed on each side in a rotation direction of the thrust plate, sufficient oil can be stored in both oil sumps, so that during starting of the engine preferable oil supply and lubrication may be achieved for the thrust plate.